1. Field of the Invention
The invention relates to pneumatic impact devices. In particular, the present invention relates to pneumatic percussion power tools.
2. Description of the Related Art
Pneumatic power tools are known in the art. Exemplary of the pneumatic power tools of the prior art are those disclosed in the following U.S. Patents:
U.S. Pat. No. 4,823,886 discloses a vacuum-compression type percussion power tool including a housing, a cylinder fixed in the housing, a piston reciprocating in the cylinder from a reciprocating drive mechanism such as a crank mechanism driven by an electric motor, or any other suitable drive, a working tool installed in the front part of the power tool, and a floating striker which slides inside the cylinder in a space between a tail portion of the working tool and the lower end of the piston. The power tool has a sealed auxiliary chamber which is formed by means of a hollow casing which surrounds the cylinder, and a space below the striker. The auxiliary chamber is connected to a main working chamber, which is formed between the piston and a striker, through a set of compensation holes and a set of idle-stroke holes. A check valve is installed in the wall of the auxiliary chamber. This check valve, which connects the auxiliary chamber with an atmospheric-pressure space between the housing and the cylinder, allows flow of air in a direction only from the above-mentioned atmospheric-pressure space to the auxiliary chamber. As a result, during several cycles after starting the power tool, an additional quantity of air will be sucked into the auxiliary chamber via the check valve, so that after reaching established conditions, the auxiliary chamber and the main chamber will operate with an increased pressure at the commencement of each cycle. This will increase the energy of impact.
U.S. Pat. No. 4,651,833 discloses a pneumatic impact tool wherein a two-stage piston is reciprocable in the two-stage chamber of a cylinder. The tool which is to penetrate into a bone is mounted in the front portion of the cylinder and the piston strikes against such front portion in response to admission of compressed air against its rear end face. A relatively small annular shoulder of the piston faces forwardly and is continuously acted upon by compressed air. When the piston approaches or reaches the end of its forward stroke and rebounds from the front end portion of the cylinder, it seals the source of compressed air from its rear end face so that the action of compressed air upon the shoulder suffices to propel the piston rearwardly against the rear end portion of the cylinder at which time the piston reestablishes a path for the flow of compressed air against its rear end face so that is propelled forwardly against the front end portion of the cylinder.
U.S. Pat. No. 4,213,301 discloses a compressed air apparatus for driving fastening elements, such as bolts and nails, into receiving material, including a first or driving piston mounted in a first chamber through which it is axially displaceable. A pressure converter arrangement is connected to an inlet to the first chamber for supplying the compressed air required for displacing the first piston for driving in a fastening element. The pressure converter includes a storage chamber, a second chamber in communication with the storage chamber and a third chamber. A double headed piston has one head in the second chamber and the other head in the third chamber. The third chamber has a much greater transverse cross-sectional area than the second chamber. Compressed air supplied to the third chamber compresses air in the second chamber which is directed into the storage chamber. From the storage chamber, the compressed air is charged into the first chamber for driving the first piston forwardly for inserting the fastening element.
U.S. Pat. No. 3,005,443 discloses a rock drill which is a pressure fluid actuated percussive type tool including a casing, a pressure fluid actuated piston reciprocable forwardly and rearwardly in the casing, a working implement positioned to be actuated by the piston, a fluid distributing device to distribute fluid to the interior of the piston, and a control device to control the distribution of fluid to move the piston rearwardly substantially slower than in the forward direction, and to momentarily delay the piston during its rearward stroke.
U.S. Pat. No. 1,092,237 discloses a pneumatic tool, a cylinder, a piston reciprocally mounted in the cylinder, a valve housing, a shoulder formed in the valve housing, a shoulder formed in the valve housing, a valve piece mounted in the valve housing for controlling the induction of the motive fluid, the valve piece including a hollow member having an annular flange at each extremity, one of the flanges being arranged to close off the induction of the motive fluid to the rear of the piston when the valve piece is in one position, while the other flange is arranged to establish communication of the motive fluid with the cylinder in front of the piston, the last named flange adapted to rest upon the shoulder of the valve housing while the valve piece is in position to establish communication of the motive fluid with the cylinder in front of the piston, and the last named flange having a relatively small opening therethrough adapted to permit the motive fluid to escape from the rear of the valve piece when the latter moves rearwardly.
U.S. Pat. No. 919,270 discloses a hammer drill including a cylinder member having a piston chamber, a piston operating therein, and a control device for controlling the supply of motive fluid to and its exhaust from the cylinder member, the control device including a movable valve having an exhaust passage that opens through both ends thereof and a stationary closure plug for one of the open ends, the valve being movable into and out of connection with the plug.
U.S. Pat. No. 917,242 discloses a pneumatic hammer including a throttle valve and a device for automatically opening the valve by motive fluid pressure upon pressing the tool to its work.
U.S. Pat. No. 855,975 discloses a pneumatic tool including a valve box, a chambered valve therein communicating at its ends with the interior of the valve box, an exhaust port leading from within the valve box at each end of the box, a piston containing cylinder, and an exhaust port or ports leading therefrom to the valve box, and being in communication with the interior of the valve, air from the exhaust port passing to the atmosphere, in part directly through one of the exhaust ports at the end of the valve box, and in part through the valve to the exhaust port at the other end of the valve box.
U.S. Pat. No. 703,758 discloses a pneumatic riveting tool with a casing provided with supply channels and ports, including a handle at one end of the same, a tool guided in the opposite end of the casing, a piston-valve located at the interior of the casing, the piston-valve being hollow and provided with circumferential grooves and an opening in one of the grooves, a return-channel connecting the rear end of the casing with the front end a cushioning-spring located between the piston-valve and handle, a channel connecting the interior of the casing with the space behind the valve, and shoulders at the rear end of the casing for arresting the spring and the piston-valve in their forward motion, substantially as set forth.